Quantifying the Impact of Thermal Gradients on Electromigration Lifetimes in 90 nm CD Cu Lines

The interaction between thermomigration (TM) and electromigration (EM) in 90 nm CD Cu lines is studied. First, the key physical parameters of TM are assessed: E<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</inf>=1.15 eV, D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf>=5.12×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/sec and Q*=0.16 eV. Then, for our dedicated structure, calibrated thermal models combined with analytical models and package level EM, TM and EM+TM tests show a significant impact of thermal gradients (∇T) on EM lifetimes. Using our analytical model, we predict that, for the used technology, at 125 °C, a ∇T of -0.8 °C/μm increases EM lifetimes by 10%, while a ∇T of 1.0 °C/μm decreases it by 10%.